1. Field of the Invention
The present invention relates to a communication system and communication method for the same. More particularly, the present invention relates to a multicarrier communication system for high-speed mobile communication based on multiple carriers, and to an adaptive carrier selection method and a link quality reporting method for the same.
2. Description of the Related Art
Fourth Generation (4G) mobile communication technology has adopted carrier aggregation for further evolution. Carrier aggregation enables multiple adjacent or non-adjacent Component Carriers (CC) to be used as a single frequency band so as to provide higher data transfer rates.
To transmit and receive data using multiple component carriers at the same time, the complexity of transceivers linearly increases with the number of component carriers used. That is, as the number of component carriers used in carrier aggregation increases, the complexity of transceivers increases. Hence, the maximum number of component carriers simultaneously used between a specific base station (e.g. an evolved Node B (eNB)) and a user equipment may be limited by the maximum number of component carriers simultaneously available in the base station and be set according to the capabilities of the user equipment. For efficient carrier aggregation, adaptive component carrier selection is needed that enables the base station to select component carriers preferred by a specific user equipment for data transfer. Similarly, adaptive component carrier selection is also necessary for the base station to send control information using component carriers preferred by the user equipment.
For data transfer in a communication system, schemes adaptive to channel environments are used in modulation and coding and transmit power determination. To achieve this, the base station receives reports on link quality of the whole resource region or data transport region from a user equipment. To transmit data using multiple component carriers, the base station may have to receive a link quality report for each component carrier from the user equipment. Using collected link quality information, the base station may adaptively select component carriers to be used for data transport to a particular user equipment.
A careful approach is needed for control information transport. When the transmission resource region for control information is separated from the transmission resource region for data, link quality for control information transport may differ from that for data transport. Hence, determination of component carriers for control information transport utilizing link quality information related to data transport may cause problems. In particular, when the base station selects inappropriate component carriers for control information transport, the user equipment may fail to receive control information. This may degrade transmission efficiency and cause at least one of the user equipment to malfunction and communication failure. To address such problems, if the base station receives a link quality report on the transmission resource region for control information from a user equipment, the base station may experience additional overhead. Accordingly, a feedback method to be performed by the user equipment is needed that helps the base station to select appropriate component carriers for control information transport, and a method of determining component carriers for control information transport is needed for the base station.